Electric gas lamp with glow discharge



Oct. 19 1926.

O. SCHALLER ET AL ELECTRIC GAS LAMP WITH GLOW DI SCHARGE I Filed Nov. 22, 1920 J zi'kzziars yM Patented Oct. 19, 1926.

UNITED STATES OTTO SCHALLER, OF SUDENDE, NEAR BERLIN, AND FRITZ SCHROETER, OF SCHNARGEN- DORE, NEAR BERLIN, GERMANY, ASSIGNORS TO SAFETY CAR HEATING &: LIGHT- 1,603,417 PATENT OFFICE.

ING COMPANY, A CORPORATION OF NEW JERSEY.

ELECTRIC GAS LAMP WITH GLOW DISCHARGE.

Application filed November 22, 1920, Serial No. 425,902, and in Germany October 27, 1917.

The present invention relates to gaseous conduction lamps and more particularly to lamps of this character which are adapted to be operated at the voltages common in 5 the usual electric supply systems.

An object of this invention is to provide a gaseous conduction lamp which may be readily started and operated at voltages common in ordinary electric supply circuits 1 and more particularly to provide a lamp of the above character having low candle power in order to avoid the difliculties commonly experienced in constructing incandescent lamps of relatively low cand e power.

Lamps of the above mentioned character, when constructed and designed for operation on a direct current, have to be connected to the source of direct current supply in proper relation with respect to the polarity 20 of the source. Another object of this invention is to provide a simple and automatic means for connecting a lamp of this character in proper relation to an already existing and permanently installed direct current supply.

Gaseous conduction lamps or lamps characterized by what is termed a glow discharge are generally characterized by the necessity of employing an auxiliary device or attachment for initiating the glow discharge in the lamp. Among such devices are found inductive apparatuses for producing the necessary high voltage to bring about the initial discharge in the lamp, auxiliary electrodes incorporated in the lamp, and like devices. Furthermore, such lamps usually require an entirely different construction for operation with direct currents and with alternating currents. This invention aims to avoid these disadvantages.

In accordance with this invention the electrodes or parts of the electrodes are placed in such proximity to each other that the glow discharge will immediately take place when the lamp is connected to a source of supply whose voltage is of the usual or more commonly employed magnitude. The as pressure employed, the material of the e ectrode. the surface of the cathode, the distances separating the electrodes and the general arrangement of the several parts are so chosen that a material fraction of the impressed voltage is dissipated in the cathode drop of potential and so that, therefore, the

chief source of light is obtained from that part of the discharge known as the negative glow. The relation of these factors, however, is preferably such that the disintegration of the cathode is of such small magnitude as not to materially or excessively decrease the life of the lamp. A suitable material for the cathodes and anodes is such a metal for example as aluminium or some other metal not included in those known as the precious metals. However, it is feasible also to use one of the precious metals in combination with metals of the above mentioned character or even also alloyed therewith.

In carrying out this invention along the general lines indicated above, the lamp may be operated upon both direct and alternating current. When the lamp is to be operated upon alternating current, however, the electrodes are preferably made alike in sine, form, arrangement, and material. A lamp when so constructed has the advantage that when operated upon direct current, the necessity for giving due consideration to the polarity is avoided.

In the drawings, in which we have illustrated by way of example several embodiments of our invention,

Figure 1 is a side view of a lamp constructed in accordance with our invention, certain parts .being shown in vertical crosssection for the purposes of better illustration.

Figure 2 is a side elevation partly in. section showing the device by meansof which a lamp adapted to operate upon direct current may be connected to a direct current source in proper polarity. J

Figure 2 is a vertical sectional View showing certain other features of a device such as is illustrated in Figure 2.

Figure 3 is a side elevation of a lamp adapted to be operated upon both alternating and direct currents.

Figure 4 is a plan View partly in section* of a modified form of lamp showin a possible arrangement of electrodes, an

Figure 5 is a further illustrative embodimentof a lamp shown in side elevation and partly in section; and

Figure 6 is a side view, partly in section. showing a modified form of device for conneeting a direct current lamp in proper relation to a direct current source.

followin The invention accordingly consists in the features of construction, arrangement of parts and combinations of elements as will be exemplified in the structures to be hereinafter described and the sec e of the a Y plication of which will be in icated in t e claims.

Referring now to Fig. 1 of the drawin 5, there is illustrated a vessel 1, preferably 0 a suitable glass construction, in the lower interior of which is mounted and preferably formed integrally therewith a supporting post 2. The post 2 has mounted upon it in any suitable manner an extension 3 which may take the form of a tube, for example, through which may be carried the conducting wire 4 adapted to supply. the anode which preferably takes the orm of a pluralit of outwardly and downwardly extending wires 6 suitably connected to the supply wire 4 as at 5. The cathode preferably takes the form of a cylinder 7 supported by and surrounding the extension 3 of the supporting post or pillar 2. As shown in the drawing, the cathode 7 is cylindrical and may conveniently be formed in cylindri cal shape out of a suitable sheet, for examle, of the metal which it is desired to use or the electrode. Its exterior or exposed surface is made of such area as is commensurate with the current intensity at which the lamp is to operate. The cylindrical cathode 7 is preferably supported at its lower end in position upon the insulating post 3 by means of a plurality of radially extending wires 8 in turn supported upon the bead 8 extending circumferentially about the supporting post 3. At its upper end the supporting post 3 is provided with a circumferentially extending bead 10 adapted to retain the cylindrical electrode 7 in position upon the supporting post 3. The wire 9 extending through the supporting pillar 2 is connected to the electrode 7 and forms the current supply wire for connecting this electrode to the external source of current.

A lamp thus constructed will operate on either direct or alternating current. In case the lamp is operated on alternating current, those alternations of the current supplied for which the electrode 7 is cathode are operative to bring about the luminous discharge. When, however, used on direct current, the lamp should be connected to the direct current supply system in proper polar relation, namely, in such manner that the electrode 7 is the cathode.

In order, therefore, to permit a lamp of the above type to be connected to a direct current supply system in proper polarity, it is desirable to provide the lamp with a screw plug which is smaller than the standard lamp socket and to which the conductors leading to the two electrodes may be permanently connected, as is usual in lam construction. Thus, turning now to Fig.

of the drawings, the lamp bulb indicate at 1 and having mounted therein suitable electrodes which, for the sake of simplicity, are not illustrated in this fi 'ure, is provided with a screw base having t e screw-threaded sleeve 16 and the center contact 16 to which the two electrodes of the lamp are respectively connected. The screw base, and hence the threaded sleeve 16, is smaller than the standard lamp base and is adapted to be fitted into a pole-selecting plug. The latter comprises an externally threaded sleeve 13 and an internally threaded sleeve 17 of smaller diameter insulated from one another b means of a suitable insulating material in icated at 17. The insulating material 17 interposed between the two threaded sleeves 13 and 17 is provided with a base portion 17 upon the interior of which is mounted a center contact 18 and upon the exterior of which is mounted a second center contact 18, the two center contacts 18 and 18 being insulated from one another by the interposed base portion 17 The exterior threaded sleeve 13 is made to conform to the standard Edison lamp base and is adapted to be threaded into a standard socket whose threaded sleeve is indicated at 11. When so associated with a standard Edison socket the exterior center contact 18 contacts with the interior center contact 11 of the standard Edison base.v

The threaded screw base 16 of the lamp 1 is adapted to be threaded into the poleselecting lug and is in engagement with the interior t readed sleeve 17. The center con tact 16 of the lamp thus engages the interior center contact 18 of the pole-selecting plug. In order to connect the lamp in proper polar relation to an existing direct current circuit choice may be made between two pole-selecting plugs as above described. In the one pole-selecting plug which may be chosen the interior threaded sleeve 17 is in electrical connection with the exterior threaded sleeve 13 as indicated by conductor 13. The interior center contact 18 is electrically connected with the exterior tip contact 18 as by means of the conductor 18. In the other pole-selecting plug which may be chosen according to circumstances and illustratively shown in Fig. 2 the interior sleeve 17 is in electrical connection, as by means of the conductor 13 with the exterior center contact 18; whereas the interior center contact 18 of the pole-selecting plug is electrically connected to the sleeve 13 by means of the conductor 13. Thus, it will be seen where the lamp 1 is connected by means of a pole-selecting plug to a standard Edison socket associated with a direct current supply either of the above described two pole-selecting plugs may be employed and by choosing the proper plug the lamp 1 and its associated electrodes may be connected to the direct current supply in proper polar relation. As above noted, in the two plugs described the several parts are interconnected in reverse o der as will be clear from Fig. 2 and Fig. 2. The proper plug is readily determined upon since where the lamp 1 is connected in improper polar relation to the direct current supply, the luminous effect of the lamp, if at all present, will be abnormal and readily detected, whereupon the pole-selecting plug in which the connections are reversed may be employed to reverse the connection of the electrodes to the direct current supply.

It will be noted also that lamps of the above character may be uniformly constructed, that is, the cathode may for example be consistently connected to the center contact 16 and the anode may be consistently connected to the threaded sleeve 16. Where all lamps are thus standardized in their manu facture, it will readily be seen that a poleselecting plug, when once associated wlth a given direct current supply circuit, will bring about the proper connection of a second lamp 1 when the first is displaced.

It is preferred, however, to construct the electrodes of the lamp so as to be equally effective and operable with either direct or alternating current without regard to the polarity of the direct current circuit to which the lamp may be connected. Such a construction is illustrated in Fig. 3 of the drawings wherein it will be noted that the lamp bulb 1 is provided with an interiorly extending supporting post 21 through which the conductors 22 and 23 extend. The interior ends of the conductors 22 and 23, being fused into the supporting post 21, may convemently form the supports for two electrodes 19 and 20 each in the form of a grid. Thus the electrode 19 may comprise a plurality of substantially parallel spaced conductors indicated at a and thus the electrode 20 may comprise a plurality ofsimilarly spaced and substantially parallel conductors b, which conductors b are preferably related with respect to the conductors a. of the other electrode so as to alternate therewith and to be substantially equidistant therefrom. Thus the electrodes 19 and 20 are substantially similar and symmetrical and their operation on alternating or direct current is made possible without regard to the polarity of the direct current source. When operated upon alternating current the electrodes 19 and 20, and hence the component parts a and b respectively, are alternately cathodes; and hence both electrodes are surrounded by the luminous discharge, since the eye is not sens tive enough to detect the rapid alternate operation of the electrodes as cathodes. When operated upon direct current, however, either the electrode 19 or 20 may function as a cathode. Accordingly, either of the component parts a and b of the electrodes 19 and 20 respectively are surrounded oy the luminous discharge according to which electrode functions as the cathode. The elements of that electrode which happens to be the anode will be substantially non-luminous and it will be noted that since they are preferably constructed in the form of wires they offer but an immaterial obstruction to the radiation of light from the luminous discharge to the exterior of the bulb 1.

In Fig. 4 there is illustrated a modified form which may be given thelamp constructed in general as illustrated and above described in connection With Fig. 1. In this figure there is shown in plan view a lamp bulb 1 in which is centrally positioned an electrode 19 in the form preferably of a hollow cylinder. This cylinder is preferably made of a sheet metal and constitutes the cathode. The other electrode or anode consists of a plurality of metal strips 20 grouped about the electrode 19. The individual elements 520 are suitably interconnected electrically by means of a suitable electrical conductor indicated at 20 and the electrode 19 and the interconnecting conductor 20" of the component parts 20 of the other electrode are provided with suitable conductors indicated diagrammatically at 19 and 20 for connection to a suitable electrical circuit. By arranging the elements 20 of the one electrode radially as indicated in Fig. 4, a maximum radiation or diffusion of light from the luminous region surrounding the cathode 19 is brought about since the radially positioned elements 20 offer a minimum obstruction to the passage of the light rays from the luminous region surrounding the cathode 19 to the exterior of the bulb 1. Furthermore, by this construction it is possible to maintain an equality of area in the surfaces of the two electrodes. The above described construction shown in Fig. 4 has also certain advantages in that the mechanical arrangement of the several parts of the electrodes permits of a more convenient and more practical incorporation within a lamp bulb.

In lamps of the gaseous conduction type it is oftentimes necessary to include in the circuit of the lamp a current limiting resistance. This resistance is adapted in general to function as a convenient means for maintaining the current at such a value as will maintain the luminous phenomena taking place within the lam of a gaseous conduction or luminous disc arge character and to prevent this phenomena from assuming the character of an arc. According ito this invention, a simple and convenient means is provided for housing or mounting the current limiting resistance. As above described IHII in connection with Fig. 2, pole-selecting plugs are provided for permitting a lamp of a given character to be, connected to a direct current supply circuit in proper polarity. Turning now to Fig. 6 of the drawings, there is shown a lamp indicated generally at 1 and provided with a threaded screw base 36 and a center contact 35 insulated therefrom and to which the electrodes (not shown) of the lamp 1 are respectively connected. The threadedbase 36 is adapted to be received or threaded into the interior threaded sleeve 33 of the poleselecting plug provided with the exterior sleeve 30 adapted to be threaded into a standard Edison base lamp socket. The threaded sleeve 30 is suitably insulated from the interior sleeve'33 of the plug as by means of the insulating material 32; and in a suitable circumferentially extending cavity, indicated at 37, in the insulating material 32 there is disposed the resistance wire indicated at 38. This resistance wire may conveniently be wound in position and may be connected between the elements of the pole-selecting p T hus, for example, where the lamp is primarily adapted for operation on alternating current, and Where the plug need not function as a pole selector the resistance wire 38 may be permanently connected between two of the contacting elements/in the plug so as to form part of the circuit to the electrodes of the lamp. Referring to Fig. 6. in such an arrangement the resistance wire 38 may have one of its terminals connected to the threaded sleeve or screw base 30 and may have its other terminal connected to the interior threaded sleeve 33. The electrode of the lamp 1 connected to the small threaded sleeve 36 will thus be connected to one side of the circuit through the threaded sleeve 33, the resistance 38 and, the large or standard threaded sleeve 30; the other electrode of the lamp connected to the center contact 35 will be connected to the other side of the circuit through the interior center contact 34 which is electrically connected to the exterior tip contact 31 of the plug and which, as will be understood, is adapted to make contact with the other. side of the electrical circuit.

It will also be understood, however, that where the lamp is adapted to operate primarily upon direct current so as to necessitate its connection to the direct current circuit in proper polar relation, the elements of the plug above described in connectlon with Fig. 6 may be so connected in different sets of plugs to permit the selection of the proper plug to connect the lamp to the direct current circuit in the desired manner. Thus, for example, in one set of plugs the small screw base 36 of the lamp will be connected through the interior threaded sleeve 33 electrically connected through the resistance wire 38 to the exterior standard threaded sleeve 30; whereas the center contact 35 will be in connection with the interior center contact 34 electrically connected in any suitable manner to the exterior center contact 31. In the other set of plugs, one of which may be chosen to cause a rever- 53.1 of the polar relation in which the lamp is connected to the direct current circuit, the small threaded base 36 of the lamp will be in electrical contact with the interior threaded sleeve 33 which is connected to the exterior tip contact 31 of the plug; the center contact 35 of the lamp will be electrically connected through. the resistance wire 38 to the standard threaded sleeve 30 of the plug. These connections are not illustrated in detail in Fig. 6 for the sake of simplicity and to avoid duplication and confusion in the drawings, but are believed to be clear from the above description as well as also from the description above set forth in connection with the pole selector plug described and illustrated in Fig. 2 and also in Fig. 2*. With the construction shown in Fig. 6, the lamps may be built in a simple and inexpensive manner since the resistance unit which, for the reasons above mentioned, it may be necessary to includein the circuit of the lamp need not be built int the lamp structure proper and need not, therefore, be replaced every time it is necessary to renew a lamp bulb. The resistance unit in being included in the plug which, as also above noted, may function as a pole-selecting plugymay function permanently with as many lamps as may be successively replaced or associated therewith.

In Fig. 5 of the drawings there is illustrated a modified form of gaseous conduction lamp in which the electrodes are so arranged and disposed with respect to one an other that a substantially uniform luminous glow is exposed to the eye or is available as a source of illumination. In this figure the lamp bulb 1 is provided with a centrally disposed pillar or supporting post 28 terminating at its extreme inner end in a substantially semi-spherical and hollow dome 25. The pillar 28 is preferably of glass construction as is the globe 1, and it is preferred to form the dome 25 also of glass and preferably integrally with the pillar 28. The outer surface of the dome 25 supports an electrode 24 made of a.suitable metal and formed to fit snugly over the exterior surface of the dome 25. The metallic electrode 24' is preferably of slightly greater dimension in the direction of the axis of the supporting pillar 28 than the dome 25 so that a portion thereof indicated at 24 will overlap or project beyond the end of the dome 25. A conductor 26 extending through the pillar 28 and suitably sealed therein is adapted to connect the electrode 24 to the exterior electric circuit. The other electrode of the lamp is preferably supported on the pillar 28 so as to be substantially entirely housed within the dome and preferably takes the form of a wire indicated at 27 bent in such manner that its one end will be in proximity to the interiorly exposed or rojecting portion 2 1* of the other electro e '21. A supply wire 29 extending through and fused into the supporting pillar 28 connects the electrode 27 to the other side of the exterior electrical circuit.

In the operation of the modification i1- lustrated in Fig. 5, the overlapping portion of the electrode 24 and the proximity thereto of the electrode 27 facilitates the starting of the lamp by bringing about the requisite preliminary ionization of the gaseous content. The glow discharge thereupon will coact with the entire exterior surface of the electrode 24, it being noted that the interior dome 25 upon which the electrode is supported effectively insulates the interior surface of the electrode 24 and thereby prevents the interior surface from taking part in the discharge excepting as above noted, the overlapping portion 24 facilitating the starting of the discharge and constituting but a small part of the entire effective or exterior surface of the electrode. Furthermore, the electrode 27 is substantially hidden from view in that it is positioned materially within the dome 25, and disturbing light effects taking place adjacent the electrode 27 are similarly hidden from view. The exterior surface of the electrode 24 is effective to distribute the glow discharge substantially uniformly throughout its extent so that a uniform and symmetrical source of illumination is thus provided. Furthermore, it should be noted that the construction above described is characterized by extreme simplicity mechanically and thus facilitates the ready and economical manufacture of the lamp. It may be added that Where the lamp is operated upon direct current, the electrode 24 functions as the cathode.

Considering now the gaseous content of the lamps embodying the mechanical featurcs of this invention above described, it is preferred to employ a gaseous content comprising a gas or gases of the helium group such as, for instance, helium, neon, krypton and the like. Lamps of the gaseous discharge type in which the metal of the electrodes is chosen as hereinbefore described, and which may for example be made of an alkali metal or alkali earth metal, have a. life which depends among other factors upon the rate at which the volatilization or disintegration of the electrodes, principally the cathodes, takes place. WVhere gases 0 the helium group are employed it has been found that the volatilization of the electrodes may proceed at such rates as to materially diminish the life of the lamp. However, gases of the helium group are found to materially increase the light efficiency of the lamp. It is a feature of this invention to provide against such high rates of volatilization of the electrodes, detrimental to long life of the lamp, and to make such provision without decreasing the light efficiency of the lamp.

Accordin to this invention, the gaseous content of t e lamps of the above described mechanical embodiments comprises one or more of the gases of the helium group together with small quantities of gases or vapors which may be said to be classified in groups other that the helium group. Thus, for example, a small quantity of a gas or vapor may be added to the gaseous content and for such addition such gases or vapors as hydrogen and nitrogen or compounds thereof, water vapor, carbon dioxide, metal vapors, or compounds or alloys of metals capable of vaporization. "When such an addition of a small quantity is made to the gaseous content of a gas of the helium group it has been found that the starting of the lamp and the continued operation thereof at the usual or more commonl employed circuit voltages is unimpaire and the light efiiciency, which as above noted is relatively high where gases of the helium group alone are employed, is found to be unappreciably affected. It has furthermore been found by experiment that such small quantities of gases of the general nature as those above mentioned, and among which may also be mentioned air or any of its constituents, greatly facilitate the starting or ignition of the lamp. This latter advantage is probably due to the fact that the foreign gases which are added are ionized at relatively low voltages, so that a preliminary ionization of the gaseous content is thus more readily brought about. But the principal advantage or effect resulting from the addition of the foreign gases in small quantity lies in the great reduction in the rate at which'the volatilization of the electrodes proceeds. This reduction has been found to be so great that the life of the lamp is greatly increased.

As above noted, the foreign gases are added only in small quantity. In carrying out this feature of this invention, the added gases or vapors may be introduced at the same time as is the main gaseous content which, as above noted, is preferably a gas of the helium group. A convenient manner, however, in which to introduce the required small quantity of foreign gas or vapor consists in treating the electrodes or other parts it of the lamp so as to impregnate the pores of the electrodes or other parts with sub stances which may give off the desired gas or vapor. Furthermore, the natural tendency of the glass or other material used for the globe of the lamp or for the supporting pillars, as well as also of the material of the electrodes themselves, to occlude gases or and being heated the occluded gases will be given off to mingle with the gaseous content introduced in the usual manner and will function to bring about the results and advantages above noted.

Ithas been found, however, that at low temperatures the electrodes and principally the cathode will not give off the occluded gases so that the atmosphere in which the electrodes, and the gaseous discharge operate will be substantially one composed entirely of the gas or gases of the helium group oyed. The attainment, therefore, of an em inci eased light of the lamp and of a greatly facilitated starting of the lamp is thus precluded or counteracted by the electrodes retaining the occluded foreign gases which are intended to be mingled with the main body of the gaseous content. It is therefore another feature of this invention -to add the foreign gases to the major portion of the gaseous content in such quantity that the electrodes and principally the cathode cannot occlude or absorb the entire amounts thus added and so that there remains to be mingled with the major portion of the gaseous content a suflicient quantity of the added or foreign gases or vapors over and above that occluded by the electrodes to bring about the advantages and results above set forth. The cathode or electrodes may thus be considered as saturated with the added foreign gases or vapors and the opera-. tion as above described is attained irrespective of whether the temperature of the electrodes is sufficiently high tocause the added gases to be given off therefrom.

It has further been determined that the above results and advantages may be attained more effectively if there is added to the gaseous content of a gas or gases of the helium group both a metal vapor and a foreign gas. Thus, for example, mercury vapor may be added. The electrodes of a gaseous discharge lamp have been found to occlude or absorb material quantities of mercury and hence there is included in the lamp a suflicient quantity of mercury vapor aside from that occluded by the electrodes to maintain an appreciable quantity of mercury vapor in the gaseous content over and above that occluded by the electrodes. Where such a lamp is operated at a relatively low temperature, however, the pressure of the mercury vapor may fall to detrimentally low values due to the condensation of the mercury. There is therefore added together with the mercury a suitable gas which at the correspondingtemperature will not condense, such a gas being for example, hydrogen or nitrogen. Furthermore, the mercury increases the light efiiciency of the lamp and counteracts the tendenc of the added gas to decrease the light e ciency of the lamp. The added gas acts as above mentioned to facilitate the starting of the lamp and is added in a quantity within the limit beyond which the starting of the lamp will be made more diflicult and would necessitate a higher starting voltage. It may be noted also that the mercury may be introduced in the lamp in metallic form and that in place of mercury it may also be feasible to em loy such metals as are readily vaporized, or example, potassium or alloys of such metals with mercury.

It will thus be seen that there has been provided in this invention a gaseous conduction lamp in which the several ob'ects above set forth are obtained and in w ich the advantages above noted, as well as many others, are efl'ectively achieved.

As many possible embodiments may be made of the above invention, and as many changes might be made in the embodiments above set forth, it is to be understood that all matter herein set forth is to be interpreted as illustrative and not in a limiting sense. i

We claim as our invention:

1. In a device of the class described, in combination, a glass vessel having a gaseous content of relatively high conductivity, and an anode and a cathode mounted within said vessel for maintaining therebetween a gaseous discharge when a relatively low voltage is applied thereto, said gaseous content being at such a pressure that the portion of the discharge serving as a source of light is substantially the negative glow, and said cathode being shaped to present an effective distributed surface which is outwardly convex, thereby to confine the negative glow to a substantially like form.

2. In a device of the class described, in combination, agas-filled discharge lamp for use in connection with a socket having a sleeve contact and a center contact arranged to be connected to a source of uni-directional current, said lamp having a cathode and an anode for maintaining a luminous discharge therebetween when uni-directional current is applied thereto in proper direction, and having a supporting base provided with a sleeve contact and a center contact to which said cathode and anode are connected; and means for mounting said lamp in said socket and for connecting the sleeve contact and the center contact of the base of said'lamp in proper polarity to the elements of said socket comprising one of two plugs,each including an insulating shell having upon the interior .a sleeve contact and a center contact for engagement respectively with the sleeve contact and center contact of said socket, one of said plugs having its two sleeve contacts electrically connected and its two center contacts connected electrically, and the other-having its interior sleeve contact in electrical connection with the exterior center contact thereof and its interiorcenter contact in electrical connection with the exterior sleeve contact thereof.

3. In a device of the class described, in combination, a vessel having a gaseous content of a gas of the helium group together with a small quantity of hydrogen, said gaseous content being at relatively low pressure,

' and a pair of electrodes mounted within said vessel and arranged to maintain therebetween a luminous discharge at relatively low voltage.

4. In a device of the class described, in combination, a vessel having a gaseous content including a gas of the helium group, a pair of electrodes mounted within said vessel and arranged to maintain a luminous discharge through said gaseous content at relatively low voltage, and a gas added to said gas of the helium group and forming part of said gaseous content adapted to decrease the rate of volatilization of said electrodes.

5. In a device of the class described, in combination, a vessel having a gaseous content comprising a'mixture of a gas of the helium group, a gas not included in the helium group and a metallic vapor, and a pair of electrodes mounted within said vessel and arranged to maintain therebetween a luminous discharge at relatively low voltage, said second mentioned gas having a relatively low ionization voltage thereby to facilitate the starting of the lamp and said metallic vapor acting to counteract the tendencyof said second-mentioned gas to decrease the intensity of the luminous discharge.

. 6. In a device of the class described, in combination, a vessel containing a gaseous content at relatively low pressure, a pair of electrodes mounted within said vessel and adapted to maintain a luminous discharge through said gaseous content, a base having electrically conducting elements to which said electrodes are respectively connected, said base being smaller than standard, a plug having means in which saidbase is received and havingmeans whereby said plug is received'b a standard lamp receptacle for electrical y connecting said electrodes to an electric circuit, and a resistance unit mounted within said plug and electrically interposed between one of the elements of the plug and another element thereof in electri-' I cal connection said base.

7. In a device of the class described, in combination, a lamp having a .pair of elecwith one of the elements of trodes mounted'therein and a gaseous con-- tent for providing luminous discharge in said lamp when a voltage is applied to said electrodes; a connecting base for said lamp including a sleeve contact and a center contact; and means for mounting said lamp in a lamp socket including a plug having an exterior sleeve for engagement with the sleeve of said socket, a sleeve within said'exterior sleeve and spaced therefrom for receiving and engaging the sleeve contact of said lamp base, and a resistance unit included within the space between said two sleeves of said plugand electrically interposed between two elements of said plug.

8. In a device of the class described, in combination, a lamp having a pair of electrodes mounted therein and a gaseous content for providing luminous discharge in said lamp when a voltage is applied to said electrodes; a connecting base for said lamp including a threaded sleeve contact and a center contact; and means for mounting said lamp in a screw-threaded socket including a plug having an exterior threaded sleeve con-.

tact for engaging with the threaded sleeve contact of said socket, a threaded sleeve contact within said exterior sleeve contact of @said plug and spaced therefrom and arranged to have the sleeve contact of the base of said lamp threaded into it, and a resistance unit included within the space between the two threaded sleeve contacts of said plug and electrically interposed between two elements of the latter.

9. In a device of the class described,'in combination, a vessel having a gaseous content including a gas of thehelium group, a substantially hollow electrode mounted within said vessel, a second electrode mounted within said vessel and positioned for coaction with said hollow electrode, said electrodes being adapted to maintain therebetween a gaseous discharge, and vmeans associated with' said first electrode adapted to make the interior surface thereof inactive.

10. In a device of the class described, in combination, a vessel havin a gaseous content including a gas of theIi substantially hollow electrode mounted therein, asecond electrode mounted within said vessel and positioned for coaction with said hollow electrode, said electrodes being adapted to maintain therebetween a gaseous discharge, and a non-conductive coating covering substantially the entire interior surface of said first mentioned electrode,-thereby to make the interior surface thereof inactive.

11. In a device of the class described, in combination, a vessel having a gaseous conelium group, a

tent includin a gas of the helium group, a surface of said hollow electrode adapted substantially ollow hemispherical electrode thereby to make the interior surface thereof 10 mounted therein, a second electrode mounted inactive. within said vessel and disposed substantially In testnnonywhereof we afiix our signa- 4 entirely within said hollow hemi-spherical tures.

electrode, said electrodes being adapted to v mainteintherebetween aluminous discher e, DR T SCHALIJER- and a non-conductive coating on the inter or I DR. FRITZ SCHROTER. 

